The invention relates to compositions for the production of antifouling coatings which comprise organopolysiloxanes as binder and biocides as active substance.
Antifouling coatings are used to protect articles against infestation, especially ships' hulls, screens, nets, constructions, quaysides, signalling equipment and articles which come into contact with sea water or brackish water.
Infestation growth is a severe problem especially in the case of ships, since, for example, the frictional resistance is increased and, as a consequence of the increased energy consumption and frequent spells in dry dock, the operating costs are significantly heightened. For this reason, antifouling coatings have long been used to prevent cases of infestation by algae, barnacles, tube worms, mussels or other marine organisms.
In this area it is possible to make a fundamental distinction between antifouling coatings which include biocides and those which are biocide-free.
Biocide-free antifouling coatings possess anti-adhesion properties, i.e. the intention is to prevent physically the attachment of marine organisms. U.S. Pat. No. 5 298 060, for example, describes a system based on organosilicone liquids in combination with organosilicone polymers. The effectiveness of the biocide-free antifouling coatings, however, is limited, so that within relatively short periods of time it is still necessary to carry out mechanical cleaning of the ship's hull or of the underwater construction.
Also known are antifouling coating which comprise biocides (U.S. Pat. No. 4,769,398). The biocides kill the organisms which form the infestation. Common antifouling biocides are organotin compounds or else copper antimony and bismuth compounds. The disadvantage of these biocides is their poor environmental compatibility. Antifouling biocides which include heavy metals are particularly problematic since they cause contamination of the sea water and of the sea floor, especially in the area of harbours. The purely organic biocides which are also mentioned in U.S. Pat. No. 4,769,398, on the other hand, do not have a good long-term action, since apparently the active substance is degraded prematurely while still in the coating.
The object of the present invention is therefore to provide a highly effective antifouling coating which has good long-term action and improved environmental compatibility.
It has surprisingly now been found that antifouling coatings with heavy-metal-free biocides exhibit markedly improved antifouling properties in conjunction with a good long-term action and improved environmental compatibility if organopolysiloxanes are used as binders in the antifouling coating.